Professor M.L.H. Green

Milestones in Original Research Contributions

The early days of research were in the field of synthesis and reactions of organotransition metal compounds and covered the period 1958– 2000. In 1990 research commenced on heterogeneous catalysis and was focused towards hydrocarbon reactions. And in 1993 a completely new area of research into carbon nanotubes started. The highlights of the discoveries made in these areas are listed below in chronological order. Key references are given in the text, often together with citation numbers presented as C. xxx (these were taken from the Web of Science on January 24th 2006). Those given in bold are particularly noteworthy.

Fundamental reactions of transition metal alkyl and carbene systems

The first demonstration of β-hydrogen abstraction from a metal-alkyl system, its reversibility, and its role as a model for the mechanism of metal catalysed olefin isomerisation. (12, 15, C. 186) The reversible β-elimination reaction is widely available to transition metal alkyls with β-hydrogens.

The first demonstration of a reversible alpha-elimination of a metal-methyl giving a transition metal-methylene-hydride.(112 C. 97, 159 C. 109) The reversible α-elimination reaction is widely available to transition metal alkyls with α-hydrogens.

The first systematic synthesis of metallacyclobutanes and that their decomposition occurred with carbon-carbon bond cleavage, as previously proposed for the olefin metathesis reaction mechanism. (125 C. 111 129, C. 61, 133, C. 87)

The discovery of a general route to the synthesis of hydroxycarbene derivatives of transition metals: the second paper on transition metals carbene systems. (62 C. 107)

Pioneering studies of the activation of carbon-hydrogen G-H bonds in aromatic and aliphatic hydrocarbons by transition metal compounds

A.E Shilov first showed that platinum metal systems could catalyse the H/D exchange beterrn deuterium and alkanes and made kinetuc studies, However no proposed alkyl-hydride compounds were isolated. The first demonstrations for the isolation of stable alkyl- and aryl-hydrides was made by Green, He showed the insertions of a transition metal centers into C-H bonds of both aromatic and saturated C-H aliphatic bonds. Both photochemical and thermal activation processes were used. (88 C. 78, 162 C.77, 259 C. 125)

The synthesis of the first zerovalent compounds of the early, refractory transition metal via the development of the electron-gun metal vapour synthesis experiment

Metal vapour synthesis was first shown by Peter Timms. The first demonstration of the electron gun furnace method for metal vapour synthesis, and its use for the synthesis of the first examples of zerovalent bis-eta-benzene compounds of titanium, zirconium, hafnium, niobium and tantalum. The synthesis of bis-benzenetungsten on a large scale (5-10 g) and many other metal atom reactions.(96 C. 67, 117 . 62, 186 C. 116, 255, 56, 171 C. 60, 234, C. 69)

There are now many active groups in this area. There were 53 recent articles cited under WoS search Organometallic Materials, the most highly cited of which was a review of organometallic non-linear optical materials (> 230 citations).

Pioneering studies on transition metal-hydrogen compounds

The first hydrides of tantalum and related tungsten and molybdenum compounds (with Wilkinson). (9, C.226)

The synthesis of the first stable nickel-hydride compounds – such systems had long been proposed following the discovery of nickel catalysed hydrogenation reactions by Paul Sabatier in 1913.(43) This work was one of the earliest demonstrations of the use of a bulky tertiary phosphineligands to achieve increased thermal stability, now a widely exploited strategy.

There is now appreciation of the widespread role of agostic bonds as intermediates in many key metal-hydrocarbon reactions. (218 C. 68, 222 C. 1064, 302 C. 653)

A 2014 search for the word agostic using Web of Science gave 1,549 articles published by others using this term since the concept “agostic bond” was proposed in 1983. The word “agostic” has been included in the recent edition of the Oxford English Dictionary.(222 C. 1064, 302 C. 653)

More Recent Research Programs

New Heterogeneous Catalysts for the Petrochemical and Green Energy Industries

The first catalyst for the selective Partial Oxidation of Methane to synthesis gas was discovered in Oxford in 1990. (324 C. 341, 326 C. 160, 353 C. 266) This work attracted worldwide attention and many patents. References to patents are listed in the Publications section below. A survey of the Web of Science showed that there have been 4628 articles under the search term “partial oxidation of methane” since the original report and that these publications came from >30 different countries.

The Oxford work also includes the discovery of the excellence of transition metal carbides as catalysts for hydrocarbon reforming reactions and Fischer-TropschCataysts. (472, 503, 511 C. 68, 520, 559, 563, 577, 587, 589, 632)

New carbide catalysts for hydrodesulphurisation have been discovered and patented. A superior catalyst for the oxidative removal of benzthiophenes from diesel has been identified and is being patented jointly with the company Saudi Aramco. Previously the Oxford Wolfson Catalysis Laboratory was set up in Oxford and has been supported for over 18 years by industrial collaborations. These were with the Gas Research Institute, then CANMET Energy Technology Centre - Ottawa (CETC-Ottawa), the Wolfson Foundation and most recently with Saudi Aramco.

An exceptionally active, stable, and selective cobalt carbide catalyst for the conversion of synthesis gas to hydrocarbons (Fischer-Tropsch catalysis) was discovered in Oxford and patented. A spin-off company, originally called Oxford Catalysts Ltd, but has now changed to Velocys (http://www.velocys.com) has been established to exploit the Fischer-Tropsch catalyst which produces gasoline and diesel from methane with greatly reduced sulphur content, as required by new legislation. In 2012 British Airways announced they will invest an estimate £500M over eight years to develop a plant in London to convert London rubbish into jet fuels. This plant is now under construction and Velocys is providing the equipment for the required conversion of syngas derived from the rubbish into the jet fuel (http://www.velocys.com). Recently the US government gave $72 million Velocys to build a related plant which will convert wood chips from Minnesota forests into transport fuels.

Pioneering studies on the chemistry of carbon nanotubes

This is the most recent new area of research.

It began with the discovery in Oxford of methods to open the ends of multi- and single-walled carbon nanotubes and then their subsequent filling with many materials. (Patent 415, 423 C. 461, 440 C. 71, 490 C.55, 496 C. 55, 523 C. 93, 587 C.79, 540 C. 114)

It has been shown that nano-crystals inside single wall carbon nanotubes (the worlds smallest crystals) have quite different properties from those of the bulk form of the filling material. The exceptional number of citations gathered in a short period shows the interest in this work. This programme was further supported by the British Government (EPSRC) by a £1,006,000 grant entitled “Molography”. This is a new concept whereby single wall carbon nanotubes are used to allow the determination of the relative atom positions of a single molecule in solution using modified transmission electron microscopy (with Professor A. Kirkland).

Most recently the use of wall-functionalized single wall carbon nanotubes filled with a radio isotope of iodine has been shown to locate selectively in the lungs of a mouse (with Benjamin Davis). This paper is highly cited (718).

The development of the Covalent Bond Classifiction (CBC) method.

The conception and proposal of a revolutionary approach to the classification of all covalent compounds of the elements. (444 C. 164) The ideas behind this work have a slowly but steadily received increasing acceptance and they are now taught to university students in many USA, UK and other countries. For example ,lectures are now given to stiudents at Harvaed, MIT, Caltech, Yale, Cornell, Boston inter alia and in10 of the iop UK chemistry departments. The CBC method is now used and cited in well-known text books. A recent CBC based classification of two-electron three-centre bonds has attracted attention (with G Parkin and J.C. Green). 729 It was foundthat there are four different 3c-2e bonds two of which were not previoulsy recognized. An article to assist the teaching of the CBC methodhas recently appeared..731 A website has been established to assist further expansion (http://www.covalentbondclass.org).

Publications

All the above work is described in the 732 refereed papers given in the List of Publications and List of 14 Patents. The total number of citations (May, 2014) is >30.000 and the h-factor is 83.